The present invention relates to the general field of nozzles fitted to turbomachines. It relates more particularly to reducing the jet noise generated at the outlet from separated flow nozzles of airplane turbomachines, in particular while such airplanes are taking off.
The nozzles fitted to civil airplane turbomachines are generally made up of a central body surrounded by a primary cowl forming between them a first annular channel for a primary flow. A secondary cowl surrounds the primary cowl to form a second annular channel for a secondary flow. Overall such nozzle assemblies are generally axially-symmetrical in shape.
The present invention relates to a device for reducing the jet noise at the outlet from such nozzles, in particular during takeoff when the ejection speeds of the primary and secondary flows are transonic (i.e. about 0.9 Mach), but without thereby degrading aerodynamic performance.
In order to reduce the jet noise generated at the outlet from the nozzles, it is known to encourage mixing between the primary and secondary flows coming from the turbomachine. For example, proposals have been made to provide the primary cowl of the nozzle with lobes that enable radial shear to be obtained between the primary and secondary flows so as to encourage said flows to mix. However, that type of lobed nozzle has little effect on reducing jet noise and it is not suitable for flows at transonic speeds. The slopes of the lobes are too great for such speeds, thereby giving rise to flow separation which degrades the aerodynamic performance of the nozzle.
European patent No. 1 160 439 discloses providing the nozzle cowls with chevrons in order to encourage mixing between the primary and secondary flows. Although that does reduce jet noise, installing such chevrons also tends to degrade the aerodynamic performance of the nozzle.